Abu Musab al-Zarqawi is a mysterious figure who has become notorious because of the savage cruelty with which he has treated his kidnap victims.

He heads an increasingly powerful Islamic fundamentalist movement in Iraq but little is known about him: US intelligence admits it does not even know if he has still has both legs, having supposedly had one amputated after being wounded by a US bomb in Afghanistan.

Zarqawi appears to be obsessed with personally participating in the grisly ritual of decapitating his hostages.

He sees anybody who co-operates with the US or the interim government as a potential victim. Islamic clerics who support the resistance but criticise Zarqawi’s methods are savagely denounced and two who were gunned down this week may have died on his orders.

The few people who have met Zarqawi and survived say he has a strong personality. A prison doctor who knew him when he was in jail in Jordan said he could order his followers to do things “just by moving his eyes.”

He calls his followers to battle with bloody thirsty rhetoric. On a tape recording earlier this year he says: “Oh Allah, America came with its horses and knights to challenge Allah and his message. Oh Allah, destroy the kingdom of Bush as you destroyed the kingdom of Caesar.”

He was born Ahmed Fadeel al-Khalayleh, an ethnic Palestinian, 37 years ago. After growing up in poverty in the grim industrial town of Zarqa in Jordan, he went to fight in Afghanistan in the 1980s. On his return to Jordan in 1992 was jailed for six years after guns were found in his house.

On his release Zarqawi returned to Afghanistan and later to Iraq. His name became internationally famous last year, when Colin Powell, the US Secretary State, denounced him before the UN Security Council as a link between al-Qa’ida and Saddam Hussein. No evidence for this was produced.

It was at this time that he is believed to have set up cells of his organisation Tawhid and Jihad (Unity and Holy War) in Iraq.

From February this year, US officials in Baghdad, citing a captured message from him, focussed on Zarqawi as the source of al-Qa’ida involvement in Iraq. This was largely a propaganda ploy. The US had long sought to portray the resistance to the occupation as either supporters of Saddam Hussein or foreign fighters linked to al-Qa’ida. Zarqawi’s name was brought up by US spokesmen at every press conference, as if he were the sole instigator of the guerrilla war.

The denunciations of Zarqawi by the US may, ironically, have helped him recruit men and money outside Iraq, particularly in Saudi Arabia. It also gained him popularity in some Sunni Muslim districts in Iraq. For instance when a US Bradley Fighting Vehicle was destroyed in Haifa Street earlier this month, local teenagers quickly made a black Tawhid flag and stuck it in the muzzle of the gun.

The group has claimed credit for a ruthless bombing campaign as well as the deaths of several hostages. The exact number of its members is unknown, but they may number as many as 1,000. It has disregarded calls by other Iraqi resistance groups to stop killing Iraqi policemen and young men, desperate for employment, queuing up to get jobs in the security services. Any Iraqi co-operating with the occupation in any way is a target.

Most of the Iraqi resistance is home-grown but Zarqawi and Tawhid plays an increasingly important role. At the time of the uprising in Sunni areas around Baghdad in April there were few foreign fighters, despite US claims to the contrary. Since then many foreigners have come to Fallujah, mostly from Saudi Arabia, and they are well-armed and well-financed.

Many Iraqis believe that extent and power of Zarqawi’s movement has been exaggerated by the US to discredit the resistance, though there is no doubt that Tawhid exists and is a growing force. But the savagery of its methods is creating a backlash among the other insurgents who see it as too willing to kill ordinary Iraqis.

ATTACKS ATRTRIBUTED TO ABU MUSAB AL-ZARQAWI

* 2003 Zarqawi is named as the organiser of a series of lethal bombings – from Casablanca in Morocco to Istanbul in Turkey.

* August 2003 Blamed by the US for assassination of the Shia cleric, Ayatollah al-Hakim, at a shrine in the town of Najaf, one of the bloodiest attacks in Iraq last year in which more than 50 Shia worshippers died.

* February 2004 US offers a $25m reward for the capture of Zarqawi (the original bounty on his head was $5m) after intercepting a letter which indicated he was working with al-Qa’ida to drive the US out of Iraq. Within days of the letter’s release, bomb attacks on recruiting centres for the Iraqi security forces had killed nearly 100 people.

* March 2004 Officials say he may have been behind the 11 March Madrid bombings which killed 191.

* May 2004 Zarqawi beheads the US contractor Nick Berg. The murder is broadcast on the internet.

* June 2004 Zarqawi’s group is blamed for a wave of attacks that killed more than 100 people in attacks in five Iraqi cities.